Position-sensing device for power distribution switch

Abstract

A remotely controlled actuator assembly is provided to switch a large power distribution switch used in an electrical utility power grid. The actuator of the assembly throws the switch between at least two positions to establish at least two power routing conditions. The actuator assembly includes a position-sensing device to repeatably and accurately indicate the position of the actuator. The position-sensing device generates a signal indicative of the extent of displacement of the actuator. The generated signal provides feed-back to a control system which control the extent of actuator travel.

What is claimed is: 
     
       1. An actuator assembly for use with a power distribution switch of the type used with an electrical utility power grid, the distribution switch being movable to establish at least a first and a second power routing condition, said actuator assembly comprising: an actuator having a body and an actuator shaft adapted to be coupled to a lever of the power distribution switch, said actuator shaft sliding relative to said body between at least a first position, in which the lever of the power distribution switch is positioned to establish said first power routing condition, and a second portion, in which the lever of the power distribution switch is positioned to establish said second power routing condition, said actuator shaft carrying a reference member; and   a position-sensing device attached to said actuator, said sensing device generating a signal indicative of movement of said reference member as said actuator shaft moves between said first and second positions.   
     
     
       2. The actuator assembly of claim 1, wherein said position-sensing device generates a signal indicative of the extent of displacement of said reference member relative to said actuator body. 
     
     
       3. The actuator assembly of claim 1, wherein said position-sensing device comprises a linear potentiometer which includes a wiper coupled to a finger that moves with said reference member carried by said actuator shaft. 
     
     
       4. The actuator assembly of claim 3, wherein said position-sensing device additionally comprises a biasing member positioned to bias said fingers of said potentiometer against said reference member of said actuator shaft. 
     
     
       5. The actuator assembly of claim 3, wherein said potentiometer includes a body that houses said wiper, said body being attached to said actuator body. 
     
     
       6. The actuator assembly of claim 1 additionally comprising comparator circuitry which compares said signal indicative of the motion of said reference member to a preselected signal indicative of a desired actuator stop point to determine whether the actuator travel has reached the desired stop point. 
     
     
       7. The actuator assembly of claim 1, wherein said position-sensing device is a wire-wound, analog, linear potentiometer. 
     
     
       8. The actuator assembly of claim 1, wherein said reference member comprises a radially extending projection attached to said actuator shaft. 
     
     
       9. The actuator assembly of claim 8, wherein said reference member comprises an annular collar which circumscribes said actuator shaft. 
     
     
       10. The actuator assembly of claim 9, additionally comprising a housing having a body which encloses at least a portion of said actuator with said actuator rod projecting beyond said housing, said housing further including an expandable bellow which extends between said housing body and said annular collar so as to seal said portion of said actuator within said housing body. 
     
     
       11. The actuator assembly of claim 1, additionally comprising a housing having a body which encloses at least a portion of said actuator with said actuator shaft sliding relative to said body through an aperture of said body. 
     
     
       12. The actuator assembly of claim 11, wherein said housing additionally includes a bellow which extends between said body and said actuator shaft to generally seal said aperture of said body, said bellow adapted to expand and to contract as said actuator shaft moves between said first and second positions. 
     
     
       13. The actuator assembly of claim 12, wherein said reference member comprises an annular collar which circumscribes said actuator shaft with one end of said bellow connected to said annular collar. 
     
     
       14. A method of controlling the position of a power distribution switch between at least two power routing conditions, comprising the steps of: coupling an actuator shaft to the power distribution switch such that movement of said actuator shaft moves a lever of the power distribution switch;   attaching a reference member to said actuator shaft;   moving said actuator shaft to throw the power distribution switch;   continuously detecting the movement of the reference member as the actuator shaft moves;   generating a signal indicative of the movement of the reference member;   communicating said signal to control circuitry; and   comparing said signal to a preselected signal indicative of a desired actuator stop point to determine whether the actuator travel has reach the desired stop point.   
     
     
       15. An actuator assembly for use with a power distribution switch of the type used with an electrical utility power grid, the distribution switch having a movable lever, said actuator assembly comprising a motor which moves a linear actuator through a drive train, said actuator having a body and an actuator shaft, said actuator shaft moving relative to said actuator body between a first position and a second position with an end of the actuator shaft being adapted to be coupled to the lever of the power distribution switch, control logic driving said motor, and a sensor continuously detecting an electrical characteristic, independent of the motion transferred through said drive train, as said actuator shaft moves between said first and second positions, said electrical characteristic being indicative of the extent of displacement of said actuator shaft relative to said actuator body, said sensor generating a signal indicative of the position of said actuator shaft relative to said actuator body, said control logic receiving said signal from said sensor. 
     
     
       16. An actuator assembly as in claim 15, wherein said sensor is adapted to detect changes in electrical resistance. 
     
     
       17. An actuator assembly as in claim 16, wherein said sensor comprises linear potentiometer which includes a wiper coupled to a finger, said finger cooperating with said actuator shaft such that said finger and said actuator shaft move together generally in parallel. 
     
     
       18. An actuator assembly as in claim 17, wherein said actuator shaft carries a reference member and said sensor additionally comprises a biasing member positioned to bias said fingers of said potentiometer against said reference member. 
     
     
       19. An actuator assembly as in claim 18, wherein said reference member comprises an annular collar which circumscribes said actuator shaft. 
     
     
       20. An actuator assembly as in claim 17, wherein said potentiometer includes a body that houses said wiper, said body being attached to said actuator body. 
     
     
       21. An actuator assembly as in claim 15, wherein said control logic comprises comparator circuitry which compares said signal indicative of the movement of said actuator shaft to a preselected signal indicative of a desired actuator stop point to determine whether the actuator travel has reached the desired stop point.